Abstract
In the present work, we have synthesized a series of Ca (1-X) Zn2 (PO4)2: X Dy3+ (X = 0.02, 0.04, 0.06, 0.08, 0.10) white light emitting phosphors via solid state reaction method. We account the structural and photoluminescence properties of all the prepared samples. The formation of CaZn2(PO4)2 was confirmed through X-ray diffraction and Fourier transform infrared spectra analyses. The luminescence properties of the phosphor materials were investigated through optical absorption and photoluminescence studies. The details of radiative properties were obtained through Judd- Ofelt intensity parameters and they were found to follow the trend Ω2 > Ω4 > Ω6. The samples were efficiently excited under near ultraviolet radiations to get excellent white light emission in terms of color rendering and luminous efficacy. Photo luminescent spectra of all the samples exhibit two prominent peaks in blue (474 nm) and yellow (572 nm) regions corresponding to the transitions 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 respectively. It is also revealed that the luminescence intensity is maximum for the sample Ca(0.96)Zn2(PO4)2:0.04 Dy3+. The phosphor was characterized by high values of branching ratio and stimulated emission cross section for the 4F9/2 → 6H13/2 transition. The emission spectra were also analyzed using Commission Internationale de l’eẤclairage 1931 standard to understand the quality of white light emission. The chromaticity color coordinates of all the samples fall within the white light domain. The photoluminescence life time values of the 4F9/2 excited level was measured by exciting Dy3+ ions at 349 nm and was found to be 0.884 ms for the sample with optimum concentration. The internal quantum efficiency was also calculated and observed to have a very good value of about 74.9%.The present study confirms the Dy3+ doped CaZn2(PO4)2 phosphors to be a promising material for white light emitting diodes.
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